Polyalkylene glycol (PAG) is a kind of synthetic lubricant oil resulting from the polymerization of an alcohol, serving as a starting material, by the addition of ethylene oxide or propylene oxide, and is configured to have a hydroxyl group (—OH) or an alkyl group at the terminal thereof.
Such polyalkylene glycol has already been commercialized as refrigeration oil for air conditioners for vehicles by Idemitsu Kosan (Japan) and the like, and is sold in the global automotive OEM industry and on secondary markets.
However, polyalkylene glycol having a terminal hydroxyl group (—OH) has a high ability to absorb water in the air due to the hydroxyl group (—OH) during its use as refrigeration oil in air conditioners, and thus its freezing point is increased by the water absorbed to the refrigeration oil, and parts of the air conditioners may corrode. With the goal of solving the above problem, attempts have been made to substitute the terminal hydroxyl group of polyalkylene glycol with an alkyl group.
A conventional technique for alkylating the terminal hydroxyl group (—OH) of polyalkylene glycol with a methyl group is known to be a method of alkylating the terminal of polyalkylene glycol with a methyl group using, as an alkylating agent, a methyl halide such as CH3Cl, CH3I or the like (U.S. Pat. No. 4,587,365). However, this method is environmentally disadvantageous because the acid generated during the reaction has to be neutralized with a neutralizing agent and the resultant salt has to be removed, and the reaction itself is slow and completion of the reaction may become problematic. Furthermore, CH3Cl, CH3I, etc., used as the alkylating agent, are materials that are known to strongly influence global warming potential or that are expensive and hazardous, and thus the practical application thereof is limited.
Also, European Patent Publication No. 0302487 discloses a method of alkylating the terminal of polyalkylene glycol with a methyl group using methyl sulfate as an alkylating agent, in which the reaction is faster than when using methyl halide as an alkylating agent, but methyl sulfate is also known to be a hazardous material and is thus regarded as environmentally unfriendly.
Furthermore, methods of introducing an allyl group to the terminal hydroxyl group (—OH) of polyalkylene glycol (U.S. Pat. Nos. 3,408,321 and 3,951,888) are available, but are characterized by high cost and low reaction rate, making it difficult to achieve practical application thereof.